Generally, the main structure of liquid crystal displays (LCDs) comprises a front panel and a back-light module wherein the front panel comprises, for example, indium tin oxide (ITO) conductive glass, liquid crystal compounds, alignment films, color filters, polarizing films, driving ICs etc. and the back-light module comprises, for example, lamps, light guides, various optical films etc. For achieving better viewing angle and color performance in LCDs, many attempts have been made in this field, for example, the brightness of LCDs can be increased by increasing the number of the lamps. However, this makes excess heat stored in the liquid crystal displays and adversely affects the life and quality of the other elements. Also, this increases the power consumption and therefore the requirement of off-line use of an information product with the aid of a battery cannot be satisfied. Currently, increasing the panel brightness by maximizing the efficiency of the light source through the use of various optical films in back-light module, without the need of modifying any other element or design or the need of extra energy consumption, has become the most effective and simplest solution.
Brightness enhancement films are also called prism films in this industry, which have the structure of microprisms formed by curing a specific acrylic resin with high energy UV light on a polyester optical film in a thickness of 50-200 μm. The major function of brightness enhancement films is to collect the lights scattered by light guides through refraction and total internal reflection and converge the collected lights in a direction within on-axis ±35° so as to increase the brightness of LCDs.
Currently, there are many patents and literatures published and dealt with how brightness enhancement films are used in back-light modules, for example, WO 96/23649 in the name of 3M company discloses a method for preventing groove tip deformation in a brightness enhancement film comprising heating prism films to a temperature higher than or equal to the glass transition temperature of the polymer so as to increase the hardness of the groove tips. However, as shown in FIG. 1 of the present invention, the brightness enhancement film has brightness-enhancing structure on only one surface with the lower surface being smooth, that is, no scratch-resistant treatment is carried out, and thus the lower surface is easily damaged during processing and accordingly, the optical performance of the brightness enhancement film is adversely affected.
For overcoming the disadvantages mentioned above, the invention provides a brightness enhancement film as detailedly described below. As shown in FIG. 2 of the present invention, the lower surface of the brightness enhancement film according to WO 96/23649 is further coated with a coating composition comprising inorganic microparticles and then cured. The coating layer comprising inorganic microparticles not only can increase the hardness of the lower surface of the brightness enhancement film but also can prevent the surface from being scratched during processing. As a result, a better optical performance is obtained.